1. Field of the Invention
The present invention relates to a visual line detecting device and, more particularly, to a visual line detecting device which detects the direction of the visual line of a viewer's eyeball from the location of a Purkinje's first figure and the position of the center of the pupil.
2. Description of the Related Art
Conventional visual line detecting devices, such as the device disclosed in Japanese Patent Publication No. 61-172552, typically utilize a luminous point source to light the eyeball wherein light is reflected on the cornea surface to form a virtual image. The position of the center of the pupil is detected from the boundary between the pupil area and the iris area based on the differences between the reflectance of the pupil area and the iris area. An eyeball's rotational angle can then be determined based on relative movement between the reflected virtual image and the position of the center of the pupil.
A conventional visual line detecting device is illustrated in FIG. 13. A reflected image 141 from a point source (not illustrated) is reflected on the cornea surface of eye 140. From the use of image forming lens 142, eye image 144 of eye 140 and point source image 145 of a reflected image 141 are projected on the surface of an optically composed virtual light receiving element 143.
Although a virtual image of reflected light on the cornea surface moves both vertically and horizontally in accordance with the movement of the eyeball, only a small dot-like image (as compared to the total amount of light luminated) is formed on light receiving element 143. For example, see "dot-like" point source image 145.
As illustrated in FIG. 13, point source image 145 reflected from the cornea surface is often formed away from light receiving element 143. Therefore, the detection of images reflected from the cornea surface by light receiving element 143 is sometimes prohibited.
Additionally, as the position of the center of the pupil is obtained by detecting the boundary between the pupil area and the iris area based on differences between the reflectance of the pupil area and the iris area, a conventional visual line detecting device must catch slight differences of reflectance between the pupil area and the iris area, thereby requiring a multiple division photographic element with a large number of pixels for use as light receiving element 143. This can increase system cost and processing time.
If a second dimension photographic element is used as a multiple division light receiving element with a large number of pixels, a problem arises in which the processing speed slows down in proportion to the number of pixels, thereby increasing the requirement for a larger memory.
On the other hand, if a first dimension light receiving element is used, the processing speed is fast and the memory requirement is smaller; however, as discussed above for FIG. 13, there is a problem in that the reflected image on the cornea surface often forms away from the first dimension photographic element.